


Anatomy Lesson

by Fledhyris



Series: Sea Verse [3]
Category: Supernatural
Genre: Altered Anatomy, Alternate Universe - Canon Divergence, But he still has a penis, Dirty Talk, Explicit Sexual Content, First Time, Fur, I gave Dean a Mangina!, M/M, Merman Dean Winchester, Oral Fixation, PWP, Past Jessica Moore/Sam Winchester, brief mention/sexual comparison
Language: English
Status: Completed
Published: 2019-07-22
Updated: 2019-07-22
Packaged: 2020-07-10 19:15:41
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,974
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19910815
Author URL: https://archiveofourown.org/users/Fledhyris/pseuds/Fledhyris
Summary: Sam suddenly finds himself wondering where Dean keeps his penis. Some interesting details of Dean's new anatomy are revealed. Not entirely your usual m/m sex although Dean definitely does still have a penis.I honestly thought this 'verse was going to be Gen, until this happened; don't blame me, blame the boys!In the immortal words of Crowley, I apologise... for NOTHING! >:)





	Anatomy Lesson

They were lying on a beach together, just a narrow strip of sand really, a watermark between sea and shore. But it was a fine day and warm, and Dean had a thing for sunbathing. Sam supposed it must get cold, being in the water all the time. Not really cold; he knew Dean was well insulated from the ocean’s bite; but it must make a welcome change to have the sun warming his skin.

They lay cross-ways to one another, Dean stretched on his back half propped on his elbows, Sam on his belly across Dean’s tail fluke, like a spotter holding him down for some serious abdominal crunches. Not that Dean needed to exercise, with his lifestyle.

Sam was fascinated by Dean’s tail, was constantly admiring it. Couldn’t get enough of touching; stroking. Dean let him, indulging Sam with lazy amusement the way he had put up with his little brother exploring his strange, inhuman (super human) hands and feet when they were children. Sam had been surprised by the tail when he first saw it. Not by the tail itself – he had known what the bargain entailed (and pardon the pun) – but by its texture. 

He hadn’t thought too hard about it at the time, his mind skittering from the enormity of what they were about to do, and more focused on getting his brother back than the precise details of the form he would return to. But if pressed to admit it, he’d expected either scales or skin, smooth and bare like the chest Dean was currently flaunting to the weak spring sun.

The first time Dean had hauled himself out of the water and Sam had gotten a proper look, he was smitten. Except for the great, leathery fluke itself, not a patch of skin showed beneath a pelt as luxurious as a seal’s. The short fur was so dense it looked like skin under water, sleek and dark as chocolate; mottling as it dried in the sun to a rich, tawny gold. 

Sam loved dogs, had always wanted one for a pet but Dad said no, they couldn’t afford the extra responsibility. Now, he cuddled up to Dean’s tail at every chance he got, petting the thick, velvet softness like he would an animal, and Dean didn’t seem to mind. It was soothing, and it was a connection between them. Most of the time, Dean was out of reach, often even out of sight; but out of the water like this, they could get close and bond.

So today, as usual, while Dean relaxed and soaked up the sun, Sam snuggled close and burrowed his hands (and sometimes his nose) into sun-warmed plush that smelled of the sea, and Dean. He traced idle patterns in the fur with a fingernail, watching the way the colours blended from gold to brown with the lie of the grain, and became absorbed in a kind of artistic project, covering Dean’s lower half with abstract lines. This led him much higher up the tail than he normally let himself explore, right to the waistline where pelt gave way to human skin and the taut, flat lines of Dean’s stomach. His curiosity was suddenly piqued. 

“Hey, Dean?” he asked, not bothering to look up; he knew he was always listening. “So um, I know this is a bit of a personal question, but; where’s your, ah, you know. Your penis?”

“Keep doing that and you’ll find out,” Dean answered in a soft series of clicks and chirps that only Sam could interpret.

Sam’s head shot up, eyes widening as he stared, fingers abruptly stilling where they rested at the edge of skin. Dean stared back, with the look of someone caught doing what he shouldn’t; a faint blush stained his cheeks and rose up to his ears.

“Sorry, bad joke, I didn’t mean – I’m sorry Sam. Please don’t...” Dean’s eyes were huge, pleading, looking scared and yet somehow sad. 

Don’t what..? Sam wondered. Don’t be mad? Freak out? Stop touching..? This sudden vulnerability was as mystifying as it was touching. Dean always used to make lewd jokes in the past, even when Sam ceased to be embarrassed. He’d never made a big deal out of one before, like he’d actually meant it and was worried about Sam’s reaction.

He flattened his palm over Dean’s stomach, keeping the pressure light and reassuring.

“It’s okay Dean,” he said softly. “I’m not… it’s okay. I was just curious.” He swallowed, suddenly thinking of another reason why Dean might be anxious. “You… you do still have one, right?”

Dean snorted, looked mildly affronted. At least it stopped him looking so vulnerable, and Sam felt something loosen and relax inside.

“Right where it’s always been, Sammy,” Dean clarified.

Well, that wasn’t… Sam looked down, confused. Stomach blended seamlessly into tail, silk of skin becoming velvet in one long, unbroken expanse of rippling muscle. It must be internal, he realised; which made sense, more hydrodynamic, and insulated from the cold. He’d never really thought about it before, but you didn’t see… bits… dangling around on other sea going mammals, after all. But that was about the extent of his knowledge, and his fingertips itched to explore, to learn something new; discover something else strange and wonderful about his beautiful brother.

Dean sighed, long suffering. “Go ahead,” he trilled, “I know you’re not going to quit staring until you find out; get it out of your system, okay? _[Pervert.]_ ” 

Sam was guessing at that last word, as they hadn’t covered it in their regular vocabulary lessons, but a lot of what Dean said was more contextual and nuanced than specific words. Sam was learning Dean more than a language, and Sam had always been good at understanding his brother. Or else he was just making up half of what Dean said, to fill in the gaps; but it seemed to work.

Sam hesitated, glancing up to be sure he had understood. Dean just shrugged, giving him a crooked smile under eyes now lazily half lidded, like it didn’t matter, what was a little anatomy lesson between brothers? So Sam shrugged too, mentally, and got to exploring.

He stroked down from Dean’s navel, following the treasure trail of human hair as it thickened and softened into fur, mapping relative distances. When he came to where it ought to be, he started probing; running his fingertips through the coat, parting the pile. There it was; a fold of skin, bulging slightly above the planes of muscle, like a vertical slit of compressed lips. He drew one finger down the line, not really thinking about what he was doing, what it must feel like, until Dean shivered and he looked up swiftly to see him watching, his gaze dark and hooded and his lips glistening as though just licked. Sam waited a moment but Dean didn’t move or say anything, so he went back to his study. 

He rubbed the pad of his thumb experimentally over the fold, in tiny caressing circles, and felt something move inside, nudging up against his touch. He could feel Dean’s breathing quicken, the fine tremors under his skin as he held himself still. Sam laid his hand across the ridge and pressed gently with middle and index fingers, scissoring them to part the skin. The fold opened, pink and wet within, and there, nestling inside, he could just see the tip of the cock, flushed and pearly with pre-come. 

It was more like investigating a girl than his own sex, and reminded him strongly, but in a painless way, of Jess. Maybe that was what prompted his next action; or maybe he had been leading up to this all along, carefully concealing his intent from his own conscious mind so he wouldn’t lose courage.

Sam bent down and, without even thinking about it, stuck his tongue right inside and licked over the shiny head. It tasted sweeter than he expected, and Dean groaned and bucked at the contact, sending a hot jag of desire through Sam’s own groin. He knew exactly what to do here, Jess had always said he was great ‘downstairs’, and he was overcome with the urge to tease Dean’s cock out of hiding so he could get a really good look at it. He went to work, flicking his tongue along the slick sides of the opening, circling around and back every so often to lap the head, which pulsed and swelled, thickening insistently against his mouth.

Dean groaned again and, “Jesus, Sammy… Fuck, that’s… Yeah, oh, God!” was the perfect encouragement (and a good thing they’d covered cursing early on in their lessons). Sam thrust deeper, seeing just how far his tongue could penetrate, sliding his mouth down over the shaft until his face was pressing into fur and his chin was sticky with Dean’s juices. He felt something down at the base like twin beads, small and firm, and explored with his tongue tip while trying to work out what they could be. Dean keened, a long, drawn out moan of pleasure, and his cock throbbed and thrust upwards, right into Sam’s eager throat. He sucked hard and slid his fingers into the wet slot of flesh, massaging the shaft, and Dean nearly exploded under him, arching up and writhing against Sam’s face.

Sam drew back, not wanting Dean to come just yet; he was enjoying this far too much, his own dick hard and leaking in his shorts. He let the cock slide out between his lips with a soft plop, and looked. Nothing like a girl now, it rose red and majestic, jutting out from its concealing folds. It wasn’t quite like a man’s either; or more correctly, not entirely human. Sam had seen his brother naked before the change and now it was shinier, leaner and more angular, as though being hidden away inside had allowed it to be stripped back to the fundamental essence of its function. It looked somehow more naked, almost obscenely wanton, and if anyone in their family was orally obsessed, it was Dean; but Sam found himself unable to resist, suddenly desperate to take the thing into his mouth again, to lick and suck and swallow until Dean’s come poured down his throat. He suited action to desire and soon had Dean shrilling wordlessly at the sky, thrashing around in the sand under Sam’s firm grip and the weight of his body.

Sam slid his fingers back down into the wet, sucking warmth of Dean’s body. It was like having a man and a woman at the same time, weirdly exciting, and it was turning Sam on like he wouldn’t have believed. He brushed along Dean’s cock, hunting again for what he realised must be his balls, small and sensitive without the external scrotum. He found them and caressed them with the tips of his fingers while lapping with his tongue at the slit of the cock in his mouth. 

Dean was panting and squirming, uttering broken words, lost out of context. His whole body was almost vibrating, pressing up against Sam’s mouth and fingers for more. Sam wrapped his other hand around Dean’s length, drawing back so only the tip was in his mouth, and started to fist him in firm, even strokes; simultaneously rubbing his balls and suckling on the head of his cock. Dean came suddenly in glorious, thick spurts and there was the salt Sam had been craving, and he swallowed greedily, wringing out every last drop. Then he stilled, holding Dean between his mouth and hands until he felt the pulsing fade and he dropped bonelessly back into the sand.

Sam let the softening member slip from his mouth, a little regretfully, but withdrew his hand and licked off the sticky residue while Dean looked on.

“You _[kinky?]_ little son of a bitch,” Dean murmured, the soft staccato of sounds caressing. “What the hell made you do that, anyway?”

“Sorry,” said Sam, a little indistinctly around his own fingers, and not at all sincerely. “Just felt like it. I don’t really know what came over me.”

Dean was quiet for a moment or two, then his body quivered with silent laughter. “Me, mostly,” he joked and Sam grinned, crawling closer and snuggling up alongside him. The movement reminded him just how hard he was and he flexed his hips, rubbing up against Dean’s tail. He looked up into Dean’s eyes, still half closed but gazing down at Sam with a strange mixture of emotions he couldn’t quite interpret. What was not there, he was very glad to see, was anger, or disgust, or regret.

“Um, I’m still… I mean, can I..?” he asked hopefully, if not very articulately, but Dean surely couldn’t miss his meaning from the way he was grinding against him.

Dean snaked an arm down and stroked his hand over Sam’s hair. “Don’t think I’m going to make a habit of this,” he chirped, “but sure. _[Hump?]_ away. Only fair.” Another new word for Sam’s lexicon.

Sam considered briefly then shucked off his shorts, pressing his groin up against Dean’s tail as he lay back down. It was all hard muscle and silken fur and felt indescribable against the heat of his throbbing dick, and he had to hold still for several moments to prevent himself from coming right there and then. 

Dean’s hand stroked gently over his hair; Sam remembered how he’d used to comb his fingers through it when they were boys, and he suffered a slight pang. The webbing between Dean’s fingers was even more pronounced now than Sam’s, and those clever, dexterous joints would never work their childhood magic again. Dean seemed to sense the mood change and he moved, wrapping his arms around Sam and pulling him up and onto him, so that they lay stomach to stomach, and Sam’s dick brushed against Dean’s where it lay, floppy and spent like a landed fish, not quite ready to retract back into its sheath.

Sam sucked in his breath sharply, poignant memories forgotten, and his dick lurched. More than anything now, what he really wanted to do, he didn’t know if it would be possible or if Dean would allow it but…

“Dean… Can I… I want to fuck you,” he whispered into his ear, his voice husky with need. “In… in there. Can I, please? Want you so much...”

“You know I’m not a girl, right?” Dean chirruped back, and Sam didn’t need to look to see that sardonic raised eyebrow. He huffed in frustration against Dean’s throat, then kissed where he’d made a spot of damp, turned it into a nibble.

“Think you just made that pretty obvious,” he murmured. Dean raised his arm and started petting Sam’s hair again.

“Well, I don’t know if it’ll fit two down there, but you can try if you like,” he said in a sing-song series of whistles.

Sam was too horny to care about anything except the fact he’d just been given explicit permission. He resumed grinding, rubbing against Dean, who stayed half hard if not fully attentive. He shoved at Dean’s jaw with his nose until he moved his head to the side, exposing more of his throat for Sam to nibble and kiss; and he wriggled his hand down between them, feeling at the lips of the slit. The fur there was damp and sticky now, dragging at Sam’s fingers. He spread the opening, feeling the answering twitch of Dean’s cock where it was squeezed beneath his stomach. Angled himself and thrust, his own cock sliding past Dean’s and into wetness. 

The angle wasn’t right, he realised; Dean really wasn’t a girl, and the opening wasn’t designed for sex. It plunged downward, rather than inward, and to gain any significant entry, Sam would have to turn around and go at it from the sixty nine position. He tried to rise, but Dean’s arm was fast around him, holding him close.

“Dean,” he panted against his neck, “gotta… move, can’t… get in from here.”

The arm tightened even more, and Dean turned his face towards Sam’s, pressed their foreheads together.

“Maybe next time, little brother,” he said, except that somehow he managed to blend the syllables for ‘brother’ with the word he’d used before which Sam had taken to mean ‘kinky’, a dolphinesque portmanteau with a special meaning, just for him. It thrilled Sam and aroused him at the same time, not least because Dean had just implied there might actually be a next time; but now was better, from Sam’s point of view, and he pouted.

“Why not now?” he almost whined, and nipped at Dean’s upper lip.

Dean moved his head back out of the way, but not far, and only momentarily. Then he leaned back in and brushed his mouth over Sam’s, gently fisting the hair at the back of his head.

“Because, little kinky!brother,” he trilled softly, “I want to hold you, and do this,” and he pressed his lips firmly to Sam’s and licked, pushing insistently with his tongue. Sam opened his mouth willingly and welcomed the tongue, thrusting at the same time to get as much friction as he could on his cock. It slid deliciously, squeezed in between Dean’s hardening member and the lips of the fold, and he rutted the shallow opening as they kissed. It wasn’t quite fucking, but it felt fantastic, and even better when Dean moved his own hand down there and slicked his fingers on his own wetness, wrapped them around both Sam and himself, and set up a slow, sure rhythm. He thrust his tongue into Sam’s mouth in time with the pull of his hand, and Sam lost himself in the steady build of sensation.

Dean was good at this, he realised, which shouldn’t come as a surprise; he’d never tried very hard to hide it when he was jerking off, which he did with a frequency that had always made Sam feel slightly inadequate, or jealous. Since they no longer shared space to sleep, Sam had even found he missed it; but whatever Dean did out in the ocean at night, he’d clearly kept in practice. Now he brought himself back to full hardness with a few deft, twisting strokes, and only the pressure of his fingers at the start of each upstroke kept Sam from going over the edge.

Dean gradually started to quicken the pace and Sam could feel his cock, pressed against his own, throbbing and twitching, and it suddenly occurred to him that Dean had come once already, but it hadn’t taken much to get him back into a state of arousal. That was hot as hell and Sam jerked forward and moaned into Dean’s mouth. Then he broke the kiss, panting lightly.

“Dean,” he groaned, “what did you call me – say it again?”

Dean grinned, darted his tongue out to lick over Sam’s lips. “Oh, you want to hear me talk dirty do you, little kinky!brother?” and this time Sam was completely sure he’d understood him correctly and moaned again, closing his eyes and throwing his head back, close to orgasm.

“I think we might need another language lesson,” Dean went on, “so I can teach you _[cock]_ and _[suck]_ and _[come]_...” Sam didn’t really grasp any of the words, he just knew from context and the lilt in Dean’s tone that they were about sex, and he shuddered and thrust hard into Dean’s fist, and then, Christ, was Dean really saying,

“And if you’re a good boy and get an A on your test, I’ll let you fuck me, let you bury your _[cock]_ right in alongside mine until you fill me with your -”

And that was it, Sam was coming, climaxing with a shout as he strained back in Dean’s embrace, splashing his stomach and chest with ribbons of pearly whiteness; and Dean let go of his cock, but scooped up some of his seed and rubbed it around his own shaft for lubrication before picking up the pace, grunting softly as his eyes closed with effort. Sam sank down beside him, rubbing his still twitching, leaking dick into soft fur as he watched until Dean orgasmed, adding streams of his own to Sam’s in a mess all over himself.

Finally they lay together, breathing slowing, and Sam traced a finger through the cooling stickiness, swirling it over tail fur as though painting, and dipping it again and again into that fascinating wet slit until Dean grasped his wrist to make him stop.

“Kinky!brother,” he said with a smile, and leaned to claim another kiss.

“I’ve messed up your tail,” Sam observed, conversationally.

“You’ve messed up everywhere,” Dean replied, sounding a little smug. “Doesn’t matter, it’ll all come off in the sea.”

“Did we really just… do that?” Sam asked, a little awestruck, a little anxious, the tiniest bit mortified, now that the sex high was wearing off and the enormity of what they’d done hit home. He had just practically fucked his own brother; he had definitely sucked him off, and Dean had jacked him off to some filthy pillow talk. There could be no claiming any of that as accidental.

Dean just made a satisfied sounding noise in his throat and reached to pet Sam’s head again.

“No, but seriously,” Sam pursued, feeling a little panicky, “that just happened, and I don’t know… I mean I didn’t intend… And you…” He was having trouble giving voice to his churning thoughts, and frankly, he was surprised Dean wasn’t the one freaking out here, because he might refuse to talk about them but Sam knew his emotions ran deep. But,

“Thought about it for a while,” Dean admitted. “Just didn’t want to push, in case you weren’t on board.”

Sam stared.

“What? It’s not like I have much chance of finding a girlfriend.” He said it so matter of factly, but Sam felt an instant pang. He’d been so caught up in Dean’s company, jealously hoarding his brother all to himself, it hadn’t occurred to him how lonely it must be for Dean, unable to communicate or interact with anyone except Sam. He was completely cut off from all humanity, a man who had been so gregarious, so ready to joke and flirt and shoot the breeze with whomever was ready to listen.

“I’m sorry,” he said, his voice low, not really sure what he was apologising for; all of it, maybe. Bringing Dean back, like this; changing so much, without even giving him a say in the matter. 

Dean put his hand under Sam’s chin, gently forced it up until Sam met his eyes.

“Hey. Don’t apologise. I wasn’t complaining. Just telling it like it is. I’m happy, Sam; I’m alive, and what the hell more could I ask for, really? But I’ve also got you; my little kinky!loved!brother.” He said it slowly, fluting the syllables with drawn out precision to be sure Sam understood, and stroked his thumb over Sam’s lips as he spoke. The look in his eyes was tender, full of love and understanding. Sam wasn’t entirely sure he deserved it, but he was glad of it.

Impulsively, Sam threw himself against Dean, crushing him into a hug.

“Woah, steady, now you’re going to have to take a dip in the sea too,” Dean laughed softly, that soundless vibration of his chest against Sam’s. A lot of vocalisations were denied to Dean these days, but he had gained others. Apparently ‘kinky!brother’ was going to become a regular term, and Sam held the thought close as he snuggled up for some serious cuddling. Swimming could wait. Sunbathing was his new number one pastime from now on; it was going to be really great if they did this every time.


End file.
